DE102007030541A1 - Method for dosing liquid reducing agent in exhaust system of internal combustion engine, involves conveying reducing agent from dosing pump to dosing valve in rapid, sequential doses in chronologically separated, individual conveyance steps - Google Patents

Abstract

The method involves conveying a reducing agent from a dosing pump (8) to a dosing valve (10) in rapid, sequential doses in chronologically separated, individual conveyance steps to a dosing valve. The individual dosing quantities of an individual dosing process by reducing agent that are delivered in the dosing process takes place directly after the individual dosing process. The individual dosing quantities are firmly adjusted oppositively in another individual dosing process in the exhaust system. An independent claim is also included for a dosing system for dosing a liquid reducing agent in an exhaust system of an internal combustion engine.

Description

The The invention relates to a method for dosing a liquid Reducing agent in an exhaust system of an internal combustion engine with the features of the preamble of claim 1 and a hie equipped dosing system.

From the DE 10 2004 050 A1 a method for dosing a liquid reducing agent in an exhaust system of an internal combustion engine is known, in which by a metering pump, the reducing agent is conveyed in rapid succession, one after the other remote individual feed operations to a metering valve. The reductant delivered in the individual feed operations to the metering valve is either delivered from the metering valve into the exhaust system, either in time-spaced individual metering operations, or passed through the metering valve in time-spaced individual return operations and to a container for the reducing agent.

task The invention is a metering method and a dosing system of specify the type mentioned above, which is an increased Dosiermengenspreizung and in particular an extension of the adjustable Dosiermengenbereichs for reducing agent to be metered into the exhaust system small values.

These The object is achieved by a method having the features of the claim 1 and by a metering system with the features of claim 7 solved.

In the process of the invention are characterized by a appropriate design of the metering pump, preferably as a piston pump or as a diaphragm pump used by such a pump in Einzelfördervorgängen subsidized individual quantities through the dimensioning the metering pump substantially fixed. It is therefore over a determination of a number of individual dosing operations allows a high dosing accuracy. That in the individual returns facilitated by the metering valve reducing agent allows additional cooling of the metering valve. Although the inventive method also for dosing of liquid fuels, it is preferably for dosing an aqueous solution of a selective reducing agent for nitrogen oxide reduction, in particular for metering aqueous Urea solution used. Einzeldosiervorgänge and individual rewind operations are preferably carried out with a predetermined frequency of several hertz. Typical values are 20 to 50 hertz. Characteristically, they are in one another following single feed operations from the metering pump subsidized individual deliveries at least approximately same size.

According to the invention a first Einzeldosiermenge of reducing agent, which in a immediately after a single rewind operation first single metering is discharged into the exhaust system, opposite discharged into the exhaust system in other single metering operations Individually metered set adjustable.

at the method according to the invention results in a Total abgege in a certain time interval in the exhaust system Metering amount of reducing agent by the sum of the individual metered quantities of individual dosing operations performed in the time interval. The dosage can be achieved by a high ratio of Einzeldosiervorgängen to single returns in the time interval in easier Be increased. It can additionally one Increasing the frequency of the individual conveying operations be provided.

are to set small dosing, so are in proportion to the number of individual returns in one Time interval comparatively few Einzeldosiervorgänge carried out. In addition, a reduction the frequency of the individual conveying operations provided be. However, the dosing accuracy is especially for the same quantity Single dosing operations or single feed operations due to the discretization of the dosage by the Einzeldosiermengen of the reductant dispensed in single metering operations limited.

By the determination according to the invention of a first single dosage amount, in one immediately after a single rewind operation with the corresponding first Einzeldosiervorgang, opposite in other, successive Einzeldosiervorgängen in the exhaust system dispensed Einzelodosiermengen are due Avoiding the above discretization occurring inaccuracies avoided. In particular, an improved dosing accuracy is small Dosage achieved when in a first single dosing delivered first Einzeldosiermenge is set smaller than the individual dosage amounts dispensed in other single dosing operations. This results from the fact that with a small dosing quantity only one small number of Einzessosiervorgängen in the time interval and thus the size of the dosage in the time interval governed by the size of the in a time interval delivered first single dosage amount is determined.

Consequently is a by the inventive method Extension of the adjustable dosage range under extensive Maintaining the dosing accuracy especially for small values towards.

In an embodiment of the invention, the Adjustment of the first single metering by means of a reducing agent storage element with a pressure-dependent volume, which is provided between metering pump and metering valve. About the reducing agent storage element, the size of the output in the first Einzeldosiervorgang from the metering first Einzeldosiermenge is influenced. In this case, a pressure-volume characteristic of the memory element is typically decisive.

In Another embodiment of the invention is used as a reducing agent storage element with pressure-dependent volume an elastic conduit element for the reducing agent used. Preferably, this is around a feed line leading from the metering pump to the metering valve for the reducing agent or around a portion thereof.

In Another embodiment of the invention is used as a reducing agent storage element with pressure-dependent volume into a reducing agent delivery line switched-on separate hydraulic accumulator used. It can it is a membrane memory, a bladder memory or a Act piston accumulator. A spring-loaded hydraulic accumulator is preferred. The hydraulic accumulator is preferably in one of the metering pump leading to the metering flow line for the Reducing agent used. It is in terms of a highly accurate Dosing small amounts of reducing agent particularly advantageous if in a further embodiment of the invention, the hydraulic accumulator for the reducing agent provides a volume which smaller than that of the metering pump in a single conveying operation funded volume is. This is a fine adjustment allows the first single dosage.

In Another embodiment of the invention is a hydraulic pressure of the reducing agent in a connected to the metering valve Reduction agent line set adjustable. Preferably takes place the determination of the hydraulic pressure by a spring-loaded Valve against whose opening pressure the metering pump delivers. Here and below is under a spring-loaded valve to understand a valve which, after overcoming a predetermined closing force opens. Is preferred while an adjustable closing force. This can be, for example by means of a spring valve with an adjustable preload force be realized for the mechanical spring. An embodiment as an electromagnetic proportional valve with a variably adjustable Holding force for a corresponding valve closure element is also possible. The valve is preferably in one the metering valve connected to the container return line arranged.

The The object mentioned at the beginning is also solved by a dosing system, which a metering valve for delivering the reducing agent in the Exhaust system, a metering pump for the delivery of reducing agent to the metering valve via a metering pump with the metering valve connecting supply line and one from the metering valve to a container for the reducing agent guided return line comprises and for carrying out a method according to any one of the claims 1 to 6 is set up.

advantageous Embodiments of the invention are in the drawings illustrated and described below. Here are the mentioned above and to be explained below Features not only in the specified feature combination, but also usable in other combinations or in isolation, without to leave the scope of the present invention.

there demonstrate:

1 FIG. 2 is a schematic block diagram of an internal combustion engine associated with an exhaust system and a reductant dosing system; FIG.

2a . 2 B schematically illustrated temporal consequences of Einzessosiervorgängen and individual retrace operations in a preferred mode of implementation of the metering method according to the invention and

3 a schematic representation of a connected to the dosing separate hydraulic accumulator.

In 1 is schematically an internal combustion engine 1 a motor vehicle with an associated exhaust system and an associated dosing system 2 for a reducing agent, wherein the exhaust system is an exhaust pipe 4 with an exhaust gas catalyst disposed therein 3 includes. The dosing system 2 serves the metered delivery of the reducing agent in the exhaust system upstream of the catalytic converter 3 , Preferably, the internal combustion engine 1 designed as a diesel engine, and the catalytic converter 3 is as a nitrogen oxide reduction catalyst, preferably as a so-called SCR catalyst for the selective reduction of the exhaust gas of the diesel engine 1 contained nitrogen oxides (NOx) carried out. For the exhaust system further, not shown here components are preferably provided. For example, additional cleaning-effective components such as a further catalytic converter or a particulate filter and exhaust gas and temperature sensors may be provided to support the operation of the exhaust system. Is by means of a before, after or in the catalytic converter 3 arranged temperature sensor found that this leave the temperature range of its effectiveness has, so preferably a discharge of reducing agent is prevented in the exhaust gas. For example, in connection with a thermal regeneration of the exhaust gas catalyst 3 upstream particulate filter of the catalytic converter heat up such that supplied reducing agent is ineffective. In this case, the release of reducing agent into the exhaust gas is also prevented, as with excessive cooling of the catalytic converter, for example below 180 ° C.

According to the preferred embodiment of the catalytic converter 3 as SCR catalyst is the dosing system 2 for discharging a reducing agent suitable for removing NOx. Although the dosing system 2 is also suitable for metering of fuel or other liquid organic reducing agents, for example, to support a regeneration of a particulate filter, it is assumed below that it is the reducing agent is an aqueous urea solution, hereinafter abbreviated as HWL, is. For this purpose, the dosing system includes 2 a tank T, via a pipe 11 with a dosing pump 8th connected is. Via a supply line 9 can from the dosing pump 8th HWL to a metering valve 10 be encouraged. About the metering valve 10 is quantitatively controlled and as needed a finely distributed release of the HWL into the exhaust.

From the dosing pump 8th to the metering valve 10 funded and not discharged into the exhaust HWL is via a return line 12 returned to tank T.

The quantitatively controlled release of the HWL into the exhaust gas is controlled by a dosing control unit 7 controlled, which for this the metering pump 8th and one in the return line 12 arranged control valve 13 controls, which will be discussed in more detail below.

For controlling or detecting the engine operation is an electronic engine control unit 6 intended. The engine control unit 6 receives on the one hand information about significant state variables such. As speed, temperatures, pressures from corresponding sensors or sensors and on the other hand, control signals as adjustment variables to actuators such. B. issue an EGR valve or an exhaust gas turbocharger, the corresponding components are not shown for clarity. Next is the engine control unit 6 capable of injecting fuel into the engine 1 adjust as needed. For this purpose, the engine control unit 6 resort to stored maps or calculation routines.

Analogously, a detection and adjustment of operating and state variables of the exhaust system and in particular the SCR catalyst 3 performed. This task can be performed by a separate control unit or dosing control unit 7 be performed. However, it is assumed that this is also done by the engine control unit 6 is taken over.

The engine control unit 6 preferably determines, based on data available to it, for example, intake air mass flow, fuel injection pressure, fuel injection timing, EGR rate, boost pressure, intake air temperature, and optionally other quantities, a raw NOx emission of the engine 1 , The quantities mentioned can be directly from sensor signals or indirectly from characteristic curves or maps or through in the engine control unit 6 stored calculation routines are determined. Preferably, the assignment of NOx raw emission values to the relevant quantities is also stored in characteristic curves or characteristic diagrams. Further, from existing information concerning the operating state of the exhaust system from maps provided therefor, a current value of the NOx conversion capability of the SCR catalyst 3 determined.

From the information available on the NOx NOx emission values and the NOx conversion capacity of the SCR catalyst 3 and, if appropriate, further variables, a desired metering amount of the solution is determined with which an advantageous, in particular the highest possible reduction in NOx can be achieved. The information concerning the nominal metering quantity is given to the metering control unit 7 transmitted, which the metering pump 8th for a given capacity and the control valve 13 controls.

Typically, the metering pump leads 8th in a rapid, uniform and preferably constant sequence of individual conveying operations with at least approximately constant individual delivery quantities. The delivery rate of the dosing pump can 8th be changed by adjusting the pumping frequency or the frequency of individual conveying operations. Alternatively or additionally, an adjustment of the individual delivery quantities may be provided. However, it is preferable to work with constant individual delivery rates and / or a constant pumping frequency or with a setpoint throughput that is constant over time. However, it may also be provided an irregular time sequence of individual conveying operations. Subsequently, it is assumed that the metering pump 8th is designed as Konstanthub piston pump, which emits during operation of each other remote individual delivery quantities of substantially constant size.

In general, the data transmission is data cables 5 provided, which may be in the form of unidirectional or bidirectional signal lines. In particular, the engine control unit 6 and the dosing control unit 7 via a preferably designed as a so-called CAN bus data line 5 connected with each other. Furthermore, data lines from the dosing control unit 7 to the dosing pump 8th and to the control valve 13 provided, over which these are controlled.

The metering valve 10 is preferably designed as an injection valve, which automatically when reaching certain values for that of the metering pump 8th applied hydraulic pressure of the HWL opens or closes. An embodiment is preferred as a spring-loaded injection valve with a mechanical spring. On an electrical control for actuation and corresponding actuators such as a coil can therefore be omitted. If due to the metering pressure of the flow line 9 the metering valve 10 supplied HWL the closing force of a closing spring is exceeded, a valve opening is released, and the HWL is hosed. The metering valve 10 is preferably tuned with respect to the surfaces acted upon by the pressure and the closing spring so that an opening takes place only above a minimum value for the hydraulic pressure. Furthermore, an embodiment of the metering valve 10 provided such that the of the metering pump 8th HWL conveyed in a single conveying process close to the tip of the metering valve 10 is directed. In this way, the metering valve 10 be effectively cooled to the top. This is particularly advantageous if, due to the installation situation, there is an increased thermal load. This is the case when the metering valve 10 is partially flowed around by hot exhaust gas and / or is in heat transfer contact with hot exhaust pipe parts.

The metering pump designed as a Konstanthub piston pump or as a diaphragm pump 8th operates intermittently such that with a pumping frequency of preferably about 0.2 Hz to 100 Hz, more preferably with a pump frequency of 5 Hz to 50 Hz, individual conveying operations carried out, with each of which a single delivery of the HWL to the metering valve 10 is encouraged.

In order for a respective individual delivery quantity to be able to be discharged into the exhaust gas in whole or in part in a corresponding single metering process, this must be for an opening of the metering valve 10 authoritative hydraulic pressure in the supply line 9 be reached or exceeded. In the preferred embodiment of the dosing system discussed herein 2 is the position of the in the return line 12 arranged and the Dosiersteuergerät 7 correspondingly controllable control valve 13 decisive for the fact whether a single conveying operation is carried out as a single metering operation or as an individual return operation. The control valve 13 may be to allow a Einzeldosiervorgangs from Dosiersteuergerät 7 be controlled in a locked position and to enable a single return operation in a return position. In the blocking position, the return line 12 shut off, so that their flow is prevented. This may cause the opening of the metering valve 10 build authoritative hydraulic pressure, the valve opening is released and the single delivery is completely or partially delivered in a Einzeldosiervorgang as Einzeldosiermenge into the exhaust. In the return position, the return line 12 after overcoming a preferably variably predefinable or adjustable opening pressure from the control valve 13 released for a return. For this purpose, a preferably loaded with a predeterminable, in particular variably adjustable force closure element is provided, which in the return position in the flow path of the return line 12 is switched.

The metering valve 10 and the control valve 13 are executed so matched to each other that the opening pressure of the metering valve 10 is higher than the opening pressure of the control valve 13 in the return position. Overcomes therefore the dosing pump 8th in the operated in the return position control valve 13 the opening pressure of the control valve 13 so open this. Another increase in pressure is thus largely avoided, the metering valve 10 remains closed and the individual conveying process takes place as an individual return process. In this way, in the piping system of metering pump 8th to the control valve 13 during operation of the dosing system 2 constantly overpressure exists. This is preferably so high that annoying boiling or vapor bubble formation at least between metering pump 8th and control valve 13 is prevented even at elevated temperatures up to about 160 ° C to 180 ° C for the HWL.

Hereinafter, referring to the 2a and 2 B to a preferred procedure during operation of the metering system according to the invention 2 received. In this case, two sequences which are typically set in a predefinable time interval for individual return and single metering operations at a high metering quantity or a high desired throughput ( 2a ) to be metered HWL and at a small dosage ( 2 B ).

In the time charts of the 2a and 2 B is an example of a fixed distance of, for example, 50 ms performed sequence of individual conveying operations of the operating at a constant pumping frequency metering pump 8th shown. As Einzelrücklaufvorgänge effective Einzelelfördervor aisles are through open beams 20 characterized. Single metering operations effective as single metering operations are by hatched bars 21 and 21a characterized. It goes without saying that a change in the pumping frequency or the time interval of the individual conveying operations can be provided, for example, to change the throughput.

2a represents the case of the highest adjustable dosage for the corresponding pumping frequency. It is provided, even for the highest adjustable dosage at least one single conveying operation in the time interval as a single return operation 20 train. This will for the metering valve 10 even with the highest dosing a minimum cooling effect achieved by returned to the tank T HWL.

If smaller dosing quantities are to be set, a division of individual backward processes takes place 20 and single dosing operations 21 . 21a as described above by a corresponding control of the control valve 13 such that the engine control unit 6 determined target throughput of solution to be dosed at least approximately reached and dosed. In a time interval, the individual metering operations are preferred 21a . 21 carried out in direct sequence and then the individual returns 20 also in direct consequence. In each case, the same in the individual conveying operations are essentially the same, by the dimensioning or adjustment of the metering pump 8th promoted certain quantities m. Accordingly, in Einzeldosiervorgängen 21 essentially the same single metered quantities discharged into the exhaust system. An exception to this is possibly the first, directly to a single return operation 20 following single dosing 21a ,

According to the invention, it is provided that a first single metering amount of reducing agent, which is in an immediately after a single return operation 20 taking place first single dosing 21a discharged into the exhaust system, in proportion to other single metering operations 21 set in the exhaust system Einzeldosiermengen variable adjustable. In particular, it is provided, the first Einzeldosiermenge the first Einzeldosiervorgangs 21a to make a definable measure smaller than the in 2a . 2 B with 100% specified dosage forms of the other individual dosing operations 21 , In this way, the accuracy of the dosage is improved at small Dosiermengen or expanded the dosing to small Dosiermengen out.

The case of a comparatively small dosing amount is in 2 B shown. Of the 20 single-feed operations performed in the time interval, only 3 are single dosing operations 21a . 21 educated. In this case, the first single metering amount of the first single metering operation 21a by a definable measure smaller than the Einzeldosiermengen the other, following Einzeleldosiervorgänge 21 , It is immediately obvious that a more precise adjustment of the total dispensed quantity in a time interval is made possible by a variable quantification of the first single metering quantity. In particular, a small or possibly even larger first dosage form allows more accurate metering if only a small number of individual metering operations are carried out in a single time interval.

Determining the first single dosage amount of the first single delivery operation 21a can according to the invention, a hydraulic accumulator in the flow line 9 and / or in the return line 12 be turned on. The hydraulic accumulator can be designed as an elastic conduit element. For example, the flow line 9 and / or the return line 12 be formed wholly or partly of an elastic material. When switching from a single return operation 20 on the first single dosing 21a must be the hydraulic pressure due to the opposite to the control valve 13 higher opening pressure of the metering valve 10 be increased in the pipe system. Thus, the hydraulic accumulator fills and results in a smaller first Einzeldosiermenge compared to the Einzeldosiermengen the other Einzeldosiervorgänge 21 in which the hydraulic accumulator is already filled. By a targeted design of the elastic conduit member, the size of the hydraulic accumulator and thus the size of the first single metering can be set.

Alternatively, a separate hydraulic accumulator can be switched on in the line system. In this case, the flow line 9 and / or the return line 12 be rigid. 3 shows an embodiment with a in the flow line 9 switched-on separate hydraulic accumulator 30 in a schematic representation. The hydraulic accumulator 30 is in a branch of the supply line 9 arranged. Via an optionally provided shut-off valve 34 can the supply to the hydraulic accumulator 30 locked or opened. The hydraulic accumulator 30 has one by a spring or otherwise 32 loaded sliding piston 31 on. At a loading or spring force exceeding dosing of the HWL in the flow line 9 is when the shut-off valve is open 34 HWL in the hydraulic accumulator 30 pressed. It is in the hydraulic accumulator 30 pressed HWL volume on the one hand by the effective hydraulic pressure in the flow line 9 dependent. On the other hand, the volume which can be received by the hydraulic accumulator becomes a stop 33 limited. The stop 33 can be adjusted be executed, whereby the hydraulic accumulator 30 maximum recordable volume is also adjustable. This is preferably made smaller than that in a Einzeldosiervorgang 21 ejected single dosage amount corresponds.

Preferably, the holding force of the spring 32 greater than the opening pressure of the control valve located in the return position 13 equivalent. On the other hand, preferably, the holding force of the spring 32 chosen smaller than the opening pressure of the metering valve 10 equivalent. As a result of this preferred dimensioning takes the hydraulic accumulator 30 in the return valve located in the control valve 13 when performing individual returns 20 no HWL on. When switching from a single return operation 20 to a first single dosing 21a first fills the hydraulic accumulator 30 until the hydraulic pressure in the supply line 9 the opening pressure for opening the metering valve 10 has reached. If necessary, the piston already strikes before 31 at the stop 33 on and the further volume consumption of the hydraulic accumulator 30 is prevented. In a subsequent single dosing 21 is the hydraulic accumulator 30 thus at least partially filled. Due to the replenishment of the hydraulic accumulator 30 at a first single dosing 21a is thus the metering valve 10 discharged into the exhaust system first Einzeldosiermenge approximately corresponding to that of the hydraulic accumulator 30 recorded volume lower than the Einzeldosiermengen the other subsequent Einzeldosiervorgänge 21 , By a suitable adjustment of the opening pressures of hydraulic accumulator 30 , Dosing valve 10 and control valve 13 may be a small amount of the first single dosing 21a compared to other single dosing processes 21 be set adjustable. Additional degrees of freedom are by determining the maximum of the hydraulic accumulator 30 Recordable volume over the stop 33 as well as via an optional actuation of the shut-off valve 34 given.

Particularly advantageous is the possibility of the first single metering over the opening pressure of the control valve 13 in its return position. This is preferably done via an adjustable closing force of a corresponding closure element, such as a valve spring. This determines the in the supply line 9 and in the return line 12 effective hydraulic pressure when performing individual returns 20 , The transition to single dosing 21 . 21a On the other hand, the pressure rise that occurs determines, in turn, the volume of HWL absorbed by a hydraulic accumulator in the piping system and thus the shortage of the first single metering operation 21a compared to other single dosing processes 21 , Consequently, it is also possible via an adjustment of the hydraulic pressure in the supply line 9 and / or in the return line 12 during operation of the dosing system 2 be determined. An area spread is about the ratio of the closing forces or holding pressures of the closure elements of metering valve 10 and control valve 13 allows.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 102004050 A1 [0002]

Claims (7)

Method for dosing a liquid reducing agent in an exhaust system of an internal combustion engine ( 1 ), whereby by a metering pump ( 8th ) the reducing agent in rapid succession, one after the other staggered individual conveying operations to a metering valve ( 10 ) and in the individual feed operations to the metering valve ( 10 ) promoted reductant either either in time spaced apart Einzeldosiervorgängen ( 21 . 21a ) from the metering valve ( 10 ) are discharged into the exhaust system or in individual retrace operations ( 20 ) through the metering valve ( 10 ) is passed through and to a container (T) for the reducing agent, characterized in that a first single metering amount of reducing agent, which in an immediately after a single return operation ( 20 ) first single dosing ( 21a ) is discharged into the exhaust system, compared to other single dosing operations ( 21 ) is set adjustable in the exhaust gas dispensing individual Dosiermengen. A method according to claim 1, characterized in that the setting of the first single metering by means of a reducing agent storage element is carried out with a pressure-dependent volume between metering pump ( 8th ) and metering valve ( 10 ) is provided. Method according to claim 2, characterized in that that as a reducing agent storage element with pressure-dependent Volume an elastic conduit element for the reducing agent is used. A method according to claim 2 or 3, characterized in that as a reducing agent storage element with pressure-dependent volume in a reducing agent delivery line ( 9 . 12 ) activated separate hydraulic accumulator ( 30 ) is used. Method according to claim 4, characterized in that the hydraulic accumulator ( 30 ) for the reducing agent provides a volume which is smaller than that of the metering pump ( 8th ) is in a single conveying process funded volume. Method according to one of claims 1 to 5, characterized in that a hydraulic pressure of the reducing agent in a to the metering valve ( 10 ) connected reducing agent line ( 9 . 12 ) is set adjustable. Dosing system for dosing a liquid reducing agent in an exhaust system of an internal combustion engine ( 1 ), comprising - a metering valve ( 10 ) for the delivery of the reducing agent into the exhaust system, - a metering pump ( 8th ) for conveying reducing agent to the metering valve ( 10 ) via a metering pump ( 8th ) with the dosing valve ( 10 ) connecting flow line ( 9 ) and - one from the metering valve ( 10 ) to a reservoir (T) for the reducing agent guided return line ( 12 ), characterized in that the dosing system ( 2 ) is arranged to carry out a method according to one of claims 1 to 6.